Renal Safety of [177Lu]Lu-PSMA-617 Radioligand Therapy in Patients with Compromised Baseline Kidney Function

Treatment of metastatic castration-resistant prostate cancer: review of current evidence and synthesis of expert opinions on radioligand therapy

Background

Despite the boom in the development of cancer management in the last decade, most patients with metastatic prostate cancer (PCa) eventually progress to metastatic castration-resistant PCa (mCRPC) and often require multiple lines of treatment. The treatment landscape of mCRPC has evolved rapidly in recent years, introducing various types of systemic therapies, including taxane-based chemotherapy, androgen receptor pathway inhibitors, bone-targeted radionuclides (e.g., radium-223), immune checkpoint inhibitors, poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitors, and radioligand therapies (RLTs) [e.g., a prostate-specific membrane antigen (PSMA) ligand labelled with 177Lu].

Methods

To help clinicians navigate the increasingly complex treatment landscape of mCRPC, this article reviews the evidence on different therapeutic regimens from pivotal trials. In addition, it reports on the results of a questionnaire developed and distributed by the Hong Kong Society of Uro-Oncology (HKSUO), with the aim of collecting the perspectives of specialists experienced in the treatment of advanced PCa in Hong Kong with regard to the clinical application of RLT, primarily [177Lu]Lu-PSMA-617/analogue therapy.

Results

A total of 43 questionnaire respondents (including clinical oncologists, urologists, nuclear medicine specialists, and medical oncologists) voted on 27 consensus questions divided into eight sections. Consensus or strong consensus (correspondingly ≥75% or ≥90% acceptance for an answer option) was reached for 10 questions. Subsequently, a panel of 13 local and overseas experts coordinated by the HKSUO discussed the voting results and provided further insights into certain questions.

Conclusion

The literature review, the voting results of the questionnaire, and the expert opinions are expected to facilitate better understanding of recent therapeutic advancements and the role of novel RLTs in the treatment of mCRPC among clinicians.

Management of Patients with Advanced Prostate Cancer. Report from the 2024 Advanced Prostate Cancer Consensus Conference (APCCC)

BACKGROUND AND OBJECTIVE

Innovations have improved outcomes in advanced prostate cancer (PC). Nonetheless, we continue to lack high-level evidence on a variety of topics that greatly impact daily practice. The 2024 Advanced Prostate Cancer Consensus Conference (APCCC) surveyed experts on key questions in clinical management in order to supplement evidence-based guidelines. Here we present voting results for questions from APCCC 2024.

METHODS

Before the conference, a panel of 120 international PC experts used a modified Delphi process to develop 183 multiple-choice consensus questions on eight different topics. Before the conference, these questions were administered via a web-based survey to the voting panel members ("panellists").

KEY FINDINGS AND LIMITATIONS

Consensus was a priori defined as ≥75% agreement, with strong consensus defined as ≥90% agreement. The voting results show varying degrees of consensus, as discussed in this article and detailed in the Supplementary material. These findings do not include a formal literature review or meta-analysis.

CONCLUSIONS AND CLINICAL IMPLICATIONS

The voting results can help physicians and patients navigate controversial areas of clinical management for which high-level evidence is scant or conflicting. The findings can also help funders and policymakers in prioritising areas for future research. Diagnostic and treatment decisions should always be individualised on the basis of patient and cancer characteristics, and should incorporate current and emerging clinical evidence, guidelines, and logistic and economic factors. Enrolment in clinical trials is always strongly encouraged. Importantly, APCCC 2024 once again identified important gaps (areas of nonconsensus) that merit evaluation in specifically designed trials.

Mathematic Modeling of Tumor Growth During [177Lu]Lu-PSMA Therapy: Insights into Treatment Optimization

The treatment regimen for [177Lu]Lu-prostate-specific membrane antigen (PSMA) 617 therapy follows that of chemotherapy: 6 administrations of a fixed activity, each separated by 6 wk. Mathematic modeling can be used to test the hypothesis that the current treatment regimen for a radiopharmaceutical modality is suboptimal. Methods: A mathematic model was developed to describe tumor growth during [177Lu]Lu-PSMA therapy. The model examined alternative treatment schedules to maximize tumor mass reduction while still maintaining an acceptable biologically effective dose to kidneys. Median patients' pharmacokinetics from literature reports were used to obtain the dose rate over time. The model incorporates the Gompertz tumor growth and linear quadratic models to describe the effect of radiation-induced cell kill on tumor growth. For a fixed total activity of 44.4 GBq of [177Lu]Lu-PSMA-617 and a 6-wk interval between cycles, the efficacy of the standard fractionation (6-cycle) treatment schedule was compared with different treatment regimens for a distribution of published tumor masses. A treatment schedule whereby 7.4 GBq are administered in the first cycle, and the remaining activity (37 GBq) in the second cycle (1-2-cycle treatment), was examined. Results: When tumor mass nadir was used as the optimization metric, a lower tumor burden (e.g., <4 g) was insensitive to the number of cycles; the 6-cycle treatment was equivalent to the 1-2-cycle treatment. For larger masses, fewer cycles yielded better results. For a 7-g tumor, the 5-cycle, 4-cycle, 3-cycle and 1-2-cycle schedules were 24%, 50%, 76%, and 84% more efficacious, respectively, than the 6-cycle schedule. The absorbed doses to kidneys, parotid glands, lacrimal glands, and red marrow were 23, 16, 70, and 1 Gy, respectively. In all fractionated schedules, the biologically effective dose to kidneys was within tolerance (<40 Gy). Conclusion: On the basis of model-derived simulations, treatment delivered in a 1-2-cycle schedule is recommended to achieve better outcomes for patients undergoing [177Lu]Lu-PSMA therapy.

Role of Lutetium Radioligand Therapy in Prostate Cancer

Theranostics utilize ligands that chelate radionuclides and selectively bind with cancer-specific membrane antigens. In the case of prostate cancer (PCa), the state-of-the-art lutetium-177-PSMA combines the radioactive β-emitter 177Lu with Vipivotide Tetraxetan, a prostate-specific membrane antigen (PSMA)-binding ligand. Several studies have been conducted, and the therapy is not without adverse effects (e.g., xerostomia, nausea, and fatigue); however, few events are reported as severe. The available evidence supports the use of 177Lu-PSMA in selected metastatic castration-resistant prostate cancer patients, and the treatment is considered a standard of care in several clinical scenarios. Emerging research shows promising results in the setting of hormone-sensitive prostate cancer; however, evidence from high-quality controlled trials is still missing. In this review, we discuss the available evidence for the application of 177Lu-PSMA in the management of PCa patients.

Current state of theranostics in metastatic castrate-resistant prostate cancer

Prostate cancer remains one of the leading causes of cancer-related death in the world. There have been significant advances in chemotherapy, hormonal therapy and targeted therapy options for patients with castrate-resistant disease. However, these systemic treatments are often associated with unwanted toxicities. Targeted therapy with radiopharmaceuticals has become of key interest to limit systemic toxicity and provides a more precision oncology approach to treatment. Strontium-89, Samarium-153 EDTMP and Radium-223 have been trialled with mixed results. Strontium-89 and Samarium-153 EDTMP have shown benefits in palliating metastatic bone pain but with no impact on survival outcomes. Early therapeutic radiopharmaceuticals targeting PSMA that were developed were beta-emitting agents, but recently alpha-emitting agents are being investigated as potentially superior options. Radium-223 is the first alpha-particle emitter therapeutic agent approved by the FDA, with phase III trial evidence showing benefits in overall survival and delay in symptomatic skeletal events for patients. Recently, 177-Lutetium-PSMA-617 has demonstrated significant survival advantages in pre-treated metastatic castrate-resistant cancer patients in a number of phase II and III studies. Furthermore, 225-Actinium-PSMA-617 also showed promise even in patients pre-treated with 177-Lutetium-PSMA-617. Hence, there has been an explosion of radiopharmaceutical treatment options for patients with prostate cancer. This review explores past and current theranostic capacities in the radiopharmaceutical treatment of metastatic castrate-resistant prostate cancer.

Spatiotemporal modeling of radiopharmaceutical transport in solid tumors: Application to 177Lu-PSMA therapy of prostate cancer

BACKGROUND AND OBJECTIVE

177Lu-labeled prostate-specific membrane antigen (PSMA) radiopharmaceutical therapy (RPT) represents a pivotal advancement in addressing prostate cancer. However, existing therapies, while promising, remain incompletely understood and optimized. Computational models offer potential insights into RPTs, aiding in clinical drug delivery enhancement. In this study, we investigate the impact of various physiological parameters on the delivery of 177Lu-PSMA-617 RPT using the convection-diffusion-reaction (CDR) model.

METHODS

Our investigation encompasses tumor geometry and surrounding tissue, characterized by well-defined boundaries and initial conditions. Utilizing the finite element method, we solve governing equations across a range of parameters: dissociation constant KD (1, 0.1, 0.01 [nM]), internalization rate (0.01-0.0001 [min-1]), diverse tumor shapes, and variable necrotic zone sizes. This model can provide an accurate analysis of radiopharmaceutical delivery from the injection site to the tumor cell, including drug transport in the vascular, interstitial, and intracellular spaces, and considering important parameters (e.g., drug extravasation from microvessels or to lymphatic vessels, the extracellular matrix, receptors, and intracellular space).

RESULTS

Our findings reveal significant enhancements in tumor-absorbed doses as KD decreases. This outcome can be attributed to the higher affinity of radiopharmaceuticals for PSMA receptors as KD diminishes, facilitating a more efficient binding and retention of the therapeutic agent within the tumor microenvironment. Additionally, tumor-absorbed doses for KD ∼ 1 [nM] show an upward trend with higher internalization rates. This observation can be rationalized by considering that a greater internalization rate would result in a higher proportion of radiopharmaceuticals being taken up by tumor cells after binding to receptors on the cell surface. Notably, tumor shape and necrotic zone size exhibit limited influence on tumor absorbed dose.

CONCLUSIONS

The present study employs the CDR model to explore the role of physiological parameters in shaping 177Lu-PSMA-617 RPT delivery. These findings provide insights for improving prostate cancer therapy by understanding radiopharmaceutical transport dynamics. This computational approach contributes to advancing our understanding of radiopharmaceutical delivery mechanisms and has implications for enhancing treatment efficacy.

The prostate-specific membrane antigen holds potential as a vascular target for endogenous radiotherapy with [177Lu]Lu-PSMA-I&T for triple-negative breast cancer

INTRODUCTION

Overexpression of prostate-specific membrane antigen (PSMA) on the vasculature of triple-negative breast cancer (TNBC) presents a promising avenue for targeted endogenous radiotherapy with [177Lu]Lu-PSMA-I&T. This study aimed to assess and compare the therapeutic efficacy of a single dose with a fractionated dose of [177Lu]Lu-PSMA-I&T in an orthotopic model of TNBC.

METHODS

Rj:NMRI-Foxn1nu/nu mice were used as recipients of MDA-MB-231 xenografts. The single dose group was treated with 1 × 60 ± 5 MBq dose of [177Lu]Lu-PSMA-I&T, while the fractionated dose group received 4 × a 15 ± 2 MBq dose of [177Lu]Lu-PSMA-I&T at 7 day intervals. The control group received 0.9% NaCl. Tumor progression was monitored using [18F]FDG-PET/CT. Ex vivo analysis encompassed immunostaining, TUNEL staining, H&E staining, microautoradiography, and autoradiography.

RESULTS

Tumor volumes were significantly smaller in the single dose (p < 0.001) and fractionated dose (p < 0.001) groups. Tumor growth inhibition rates were 38% (single dose) and 30% (fractionated dose). Median survival was notably prolonged in the treated groups compared to the control groups (31d, 28d and 19d for single dose, fractionated dose and control, respectively). [177Lu]Lu-PSMA-I&T decreased the size of viable tumor areas. We further demonstrated, that [177Lu]Lu-PSMA-I&T binds specifically to the tumor-associated vasculature.

CONCLUSION

This study highlights the potential of [177Lu]Lu-PSMA-I&T for endogenous radiotherapy of TNBC.

Renal and Multiorgan Safety of 177Lu-PSMA-617 in Patients with Metastatic Castration-Resistant Prostate Cancer in the VISION Dosimetry Substudy

In the VISION trial, [177Lu]Lu-PSMA-617 (177Lu-PSMA-617) plus protocol-permitted standard of care significantly improved overall survival and radiographic progression-free survival compared with standard of care alone in patients with prostate-specific membrane antigen-positive metastatic castration-resistant prostate cancer. This VISION dosimetry substudy quantified absorbed doses of 177Lu-PSMA-617 in the kidneys and other organs. Methods: Participants were a separate cohort of 30 nonrandomized patients receiving standard of care plus 177Lu-PSMA-617 at 7.4 GBq per cycle for up to 6 cycles. Blood samples, whole-body conjugate planar image scintigraphy, and abdominal SPECT/CT images were collected. SPECT/CT images were collected at 2, 24, 48, and 168 h after administration in cycle 1 and at a single time point 48 h after administration in cycles 2-6. Outcomes were absorbed dose per unit activity per cycle and cumulative absorbed dose over all cycles. Cumulative absorbed doses were predicted by extrapolation from cycle 1, and calculation of observed values was based on measurements of cycle 1 and cycles 2-6. Safety was also assessed. Results: Mean (±SD) absorbed doses per cycle in the kidneys were 0.43 ± 0.16 Gy/GBq in cycle 1 and 0.44 ± 0.21 Gy/GBq in cycles 2-6. The observed and predicted 6-cycle cumulative absorbed doses in the kidneys were 15 ± 6 and 19 ± 7 Gy, respectively. Observed and predicted cumulative absorbed doses were similar in other at-risk organs. Safety findings were consistent with those in the VISION study; no patients experienced renal treatment-emergent adverse events of a grade higher than 3. Conclusion: The renal cumulative absorbed 177Lu-PSMA-617 dose was below the established limit. 177Lu-PSMA-617 had a good overall safety profile, and low renal radiotoxicity was not a safety concern. Cumulative absorbed doses in at-risk organs over multiple cycles can be predicted by extrapolation from cycle 1 data in patients with metastatic castration-resistant prostate cancer receiving 177Lu-PSMA-617.

Role of Functional SPECT and PET in Renal Emergencies

Renal scintigraphy is a centerpiece of nuclear medicine and is also commonly applied for (peri-)acute care. In this regard, referrals by the treating physician include: I.) acute obstructions caused by gradual and infiltrative tumor growth or renal off-target effects under anti-tumor treatment, II.) functional issues in infants, for example, structural abnormalities such as duplex kidneys or uroliths in adults, which can also trigger III.) Infections of renal parenchyma. Renal radionuclide imaging is also requested due to IV.) acute trauma to the abdomen, for example, to assess renal scarring or upon further follow-up after reconstructive surgery. We will discuss clinical applications of (peri-)acute renal scintigraphy, along with future prospects on the use of more advanced nuclear imaging techniques such as renal positron emission tomography.

Excellent Response to Full-Dose 177 Lu-PSMA-617 RLT in Metastatic Castration-Resistant Prostate Cancer With Transplant Kidney : A Step Ahead

ABSTRACT

177 Lu-PSMA radioligand therapy (RLT) has shown very encouraging results in metastatic castrate-resistant prostate cancer (mCRPC) patients with acceptable adverse events. The adverse events of RLT are mainly limited to salivary glands and kidneys. However, there is dearth of available data of RLT in transplanted kidney patients with mCRPC. Here is a case of 68-year-old mCRPC patient with history of renal transplant who underwent 4 cycles of 177 Lu-PSMA-617 RLT (~7.4 GBq/cycle). Posttherapy serum creatinine and glomerular filtration rate remained stable along with excellent response and symptomatic improvement, thus demonstrating the safety of full dose of 177 Lu-PSMA in renal transplant patients.

PSMA-targeted therapy for non-prostate cancers

Radioligand therapy (RLT) agents are demonstrating a crucial role in the clinical approach to aggressive malignancies such as metastatic castrate-resistant prostate cancer (m-CRPC). With the recent FDA approval of prostate-specific membrane antigen (PSMA)-targeted RLT for m-CRPC, the field has broadened its gaze to explore other cancers that express PSMA in the tumor parenchyma or tumor neovasculature. In this review article, we discuss current progress in the clinical use of PSMA RLTs in non-prostate cancers such salivary gland cancers, renal cell carcinoma, high grade glioma, and soft tissue sarcoma. We highlight early reports in small case series and clinical trials indicating promise for PSMA-targeted RLT and highlighting the importance of identifying patient cohorts who may most benefit from these interventions. Further study is indicated in non-prostate cancers investigating PSMA RLT dosimetry, PSMA PET/CT imaging as a biomarker, and assessing PSMA RLT safety and efficacy in these cancers.

Joint EANM/SNMMI procedure guideline for the use of 177Lu-labeled PSMA-targeted radioligand-therapy (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed by the majority of clinically significant prostate adenocarcinomas, and patients with target-positive disease can easily be identified by PSMA PET imaging. Promising results with PSMA-targeted radiopharmaceutical therapy have already been obtained in early-phase studies using various combinations of targeting molecules and radiolabels. Definitive evidence of the safety and efficacy of [177Lu]Lu-PSMA-617 in combination with standard-of-care has been demonstrated in patients with metastatic castration-resistant prostate cancer, whose disease had progressed after or during at least one taxane regimen and at least one novel androgen-axis drug. Preliminary data suggest that 177Lu-PSMA-radioligand therapy (RLT) also has high potential in additional clinical situations. Hence, the radiopharmaceuticals [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T are currently being evaluated in ongoing phase 3 trials. The purpose of this guideline is to assist nuclear medicine personnel, to select patients with highest potential to benefit from 177Lu-PSMA-RLT, to perform the procedure in accordance with current best practice, and to prepare for possible side effects and their clinical management. We also provide expert advice, to identify those clinical situations which may justify the off-label use of [177Lu]Lu-PSMA-617 or other emerging ligands on an individual patient basis.

Safety of Lutetium-177 prostate-specific membrane antigen-617 (PSMA-617) radioligand therapy in the setting of severe renal impairment: a case report and literature review

Reported here is a case of rapidly progressive metastatic castration-resistant prostate cancer treated with [177Lu]Lu-PSMA-617 in the setting of severe renal impairment and impending ureteric obstruction. PSMA is expressed on renal tubular cells, raising the possibility of radiation-induced nephrotoxicity, and this level of renal impairment would typically exclude the patient from [177Lu]Lu-PSMA-617 therapy. Multidisciplinary input, individualized dosimetry, and patient-specific dose reduction were used to ensure the cumulative dose to the kidneys remained within acceptable limits. He was initially planned for treatment with six cycles of [177Lu]Lu-PSMA-617. However, he had an excellent response to therapy following four cycles of treatment and the last two cycles were omitted. He has been followed for 1-year posttherapy without evidence of disease recurrence. No acute or chronic nephrotoxicity was observed. This case report highlights the utility of [177Lu]Lu-PSMA-617 therapy in severe renal impairment and provides evidence of relative safety in patients who would otherwise not be considered candidates for therapy.

Genitourinary Cancer: Updates on Treatments and Their Impact on the Kidney

Genitourinary cancers are diverse in their presentation, prevalence, and mortality risk. Although there have been significant advancements in medical (eg, immune checkpoint inhibitors and tyrosine kinase inhibitors) and surgical treatments of genitourinary cancers, patients are still at risk for chronic kidney disease, hypertension, and electrolyte derangements in the short and long term. In addition, pre-existing kidney disease may increase the risk of developing some genitourinary cancers. This review focuses on the kidney-related effects of treatments for renal cell carcinoma and bladder and prostate cancers.

Tumor Sink Effect with Prostate-Specific Membrane Antigen-Targeted Theranostics in Patients with Metastatic Castration-Resistant Prostate Cancer: Intra-Individual Evaluations

"Tumor sink effects", decreased physiological uptake of radiopharmaceuticals due to sequestration by a tumor, may impact radioligand therapy (RLT) toxicity and dosing. We investigated these effects with prostate-specific membrane antigen (PSMA)-targeted radiopharmaceuticals in the healthy organs-at-risk (the parotid glands, kidneys, liver, and spleen) of 33 patients with metastatic castration-resistant prostate cancer (mCRPC). We retrospectively performed three intra-individual comparisons. First, we correlated changes from baseline to post-RLT (after two 177-lutetium (177Lu)-PSMA-617 cycles) in total lesional PSMA (∆TLP) and organ mean standardized uptake values (∆SUVmean). Second, in 25 RLT responders, we compared the organ SUVmean post-RLT versus that at baseline. Lastly, we correlated the baseline TLP and organ SUVmean. Data were acquired via 68-gallium-PSMA-11 positron emission tomography before the first and after the second 177Lu-PSMA-617 cycle. In the parotid glands and spleen, ∆TLP and ∆SUVmean showed a significant inverse correlation (r = -0.40, p = 0.023 and r = -0.36, p = 0.042, respectively). Additionally, in those tissues, the median organ SUVmean rose significantly from baseline after the response to RLT (p ≤ 0.022), and the baseline TLP and SUVmean were significantly negatively correlated (r = -0.44, p = 0.01 and r = -0.42, p = 0.016, respectively). These observations suggest tumor sink effects with PSMA-targeted radiopharmaceuticals in the salivary glands and spleen of patients with mCRPC.

Safety and Therapeutic Optimization of Lutetium-177 Based Radiopharmaceuticals

Peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (¹⁷⁷Lu) based radiopharmaceuticals has emerged as a therapeutic area in the field of nuclear medicine and oncology, allowing for personalized medicine. Since the first market authorization in 2018 of [¹⁷⁷Lu]Lu-DOTATATE (Lutathera®) targeting somatostatin receptor type 2 in the treatment of gastroenteropancreatic neuroendocrine tumors, intensive research has led to transfer innovative ¹⁷⁷Lu containing pharmaceuticals to the clinic. Recently, a second market authorization in the field was obtained for [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto®) in the treatment of prostate cancer. The efficacy of ¹⁷⁷Lu radiopharmaceuticals are now quite well-reported and data on the safety and management of patients are needed. This review will focus on several clinically tested and reported tailored approaches to enhance the risk-benefit trade-off of radioligand therapy. The aim is to help clinicians and nuclear medicine staff set up safe and optimized procedures using the approved ¹⁷⁷Lu based radiopharmaceuticals.

2022 FDA TIDES (Peptides and Oligonucleotides) Harvest

A total of 37 new drug entities were approved in 2022; although that year registered the lowest number of drug approvals since 2016, the TIDES class consolidated its presence with a total of five authorizations (four peptides and one oligonucleotide). Interestingly, 23 out of 37 drugs were first-in-class and thus received fast-track designation by the FDA in categories such as breakthrough therapy, priority review voucher, orphan drug, accelerated approval, and so on. Here, we analyze the TIDES approved in 2022 on the basis of their chemical structure, medical target, mode of action, administration route, and common adverse effects.

Extended therapy with [177Lu]Lu-PSMA-617 in responding patients with high-volume metastatic castration-resistant prostate cancer

PURPOSE

The currently used scheme for radioligand therapy (RLT) of patients with metastatic castration-resistant prostate cancer (mCRPC) consists of 4-6 cycles of 6.0-7.4 GBq [¹⁷⁷Lu]Lu-PSMA-617 each. This standard treatment scheme has proved safe and effective resulting in objective response in most patients with no significant toxicity. Many patients, however, show high-volume residual tumor burden after the sixth cycle and may benefit from treatment continuation. Extended treatment with additional cycles has been withheld due to concerns on potential increased toxicity.

METHODS

Twenty-six patients with high-volume residual tumor burden (according to CHAARTED) after standard RLT with [¹⁷⁷Lu]Lu-PSMA-617 and no alternative treatment option received additional RLT cycles reaching a median of 10 (range 7-16) cycles with a mean activity of 7.4 ± 0.9 GBq per cycle. Response assessment with [⁶⁸Ga]Ga-PSMA-11 PET/CT was done every 2-3 cycles or if disease progression was clinically suspected or based on change in PSA value (according to the PCWG3 criteria). Toxicity was measured using routine blood work up including blood counts, liver and renal function, and was graded according to CTCAE v5.0 criteria. Survival outcome was calculated based on the Kaplan-Meier method.

RESULTS

Further PSA decline of 33 ± 28% during the extended treatment was observed in 21/26 (81%) patients, whereas 5/26 (19%) patients showed a PSA increase; correspondingly in 11/21 patients with an initial response (PR or SD) to extended cycles, treatment was discontinued due to progressive disease, whereas six (23%) patients achieved low-volume residual disease. Two (8%) patients died without showing progression, and two (8%) patients are still under therapy. The median progression-free survival was 19 (95% CI: 15-23) months, and the overall survival was 29 (95% CI: 18-40) months. Grade ≥ 3 hematological toxicities occurred in 4/26 (15%) patients during treatment extension, and nephrotoxicity (grade ≥ 3) was observed in 1/26 (4%) patient during the follow-up.

CONCLUSION

Extended radioligand therapy is a feasible treatment option in patients with high-volume residual tumor after the completion of standard treatment with six cycles of [¹⁷⁷Lu]Lu-PSMA-617. Improved survival and the acceptable safety profile warrant further investigation of the concept of additional cycles in selected patients.

Pharmacological Optimization of PSMA-Based Radioligand Therapy

Prostate cancer (PCa) is the most common malignancy in men of middle and older age. The standard treatment strategy for PCa ranges from active surveillance in low-grade, localized PCa to radical prostatectomy, external beam radiation therapy, hormonal treatment and chemotherapy. Recently, the use of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) for metastatic castration-resistant PCa has been approved. PSMA is predominantly, but not exclusively, expressed on PCa cells. Because of its high expression in PCa, PSMA is a promising target for diagnostics and therapy. To understand the currently used RLT, knowledge about pharmacokinetics (PK) and pharmacodynamics (PD) of the PSMA ligand and the PSMA protein itself is crucial. PK and PD properties of the ligand and its target determine the duration and extent of the effect. Knowledge on the concentration-time profile, the target affinity and target abundance may help to predict the effect of RLT. Increased specific binding of radioligands to PSMA on PCa cells may be associated with better treatment response, where nonspecific binding may increase the risk of toxicity in healthy organs. Optimization of the radioligand, as well as synergistic effects of concomitant agents and an improved dosing strategy, may lead to more individualized treatment and better overall survival.

Theragnostic Radionuclide Pairs for Prostate Cancer Management: 64Cu/67Cu, Can Be a Budding Hot Duo

Prostate cancer (PCa) is one of the preeminent causes of mortality in men worldwide. Theragnostic, a combination of therapy and diagnostic, using radionuclide pairs to diagnose and treat disease, has been shown to be a promising approach for combating PCa. In PCa patients, bone is one of the most common sites of metastases, and about 90% of patients develop bone metastases. This review focuses on (i) clinically translated theragnostic radionuclide pairs for the management of PCa, (ii) radionuclide therapy of bone metastases in PCa, and (iii) a special emphasis on emerging theragnostic radionuclide pair, Copper-64/Copper-67 (64Cu/67Cu) for managing the disease.

Lutetium Lu 177 vipivotide tetraxetan for metastatic castration-resistant prostate cancer

INTRODUCTION

¹⁷⁷Lu-vipivotide tetraxetan is a radiopharmaceutical that selectively targets prostate-specific membrane antigen (PSMA) and delivers beta-radiations to kill prostate cancer cells.

AREAS COVERED

Extensive experience outside the United States as well as randomized phase II and phase III data demonstrate that ¹⁷⁷Lu-vipivotide tetraxetan is a safe, generally well tolerated, and effective therapy for men with mCRPC. ¹⁷⁷Lu-vipivotide tetraxetan was approved by the FDA in March 2022 for the treatment of PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) after androgen receptor pathway inhibition and taxane-based chemotherapy based on the results of the VISION trial.

EXPERT OPINION

This review discusses the development and studies leading to the approval of ¹⁷⁷Lu-vipivotide tetraxetan. In all, ¹⁷⁷Lu-vipivotide tetraxetan is an exciting new tool in the arsenal for men with mCRPC after novel androgen pathway inhibitors and at least one taxane chemotherapy. Optimal selection of patients, sequencing of ¹⁷⁷Lu-vipivotide tetraxetan with the other agents available to treat mCRPC, and the use of dosimetry are current areas of interest with great potential and opportunities for further individual patient optimization using the tools of theranostics.

177 Lu-PSMA radioligand therapy effectiveness in metastatic castration-resistant prostate cancer: An updated systematic review and meta-analysis

BACKGROUND

An updated systematic review and meta-analysis of relevant studies to evaluate the effectiveness of prostate-specific membrane antigen (PSMA)-targeted endoradiotherapy/radioligand therapy (PRLT) in castration resistant prostate cancer (CRPC).

METHODS

A systematic search was performed in July 2020 using PubMed/Medline database to update our prior systematic review. The search was limited to papers published from 2019 to June 2020. A total of 472 papers were reviewed. The studied parameters included pooled proportion of patients showing any or ≥50% prostate-specific antigen (PSA) decline after PRLT. Survival effects of PRLT were assessed based on pooled hazard ratios (HRs) of the overall survival (OS) according to any PSA as well as ≥50% PSA decline after PRLT. Response to therapy based on ≥50% PSA decrease after PRLT versus controls was evaluated using Mantel-Haenszel random effect meta-analysis. All p values < 0.05 were considered as statistically significant.

RESULTS

A total of 45 publications were added to the prior 24 studies. 69 papers with total of 4157 patients were included for meta-analysis. Meta-analysis of the two recent randomized controlled trials showed that patients treated with ¹⁷⁷ Lu-PSMA 617 had a significantly higher response to therapy compared to controls based on ≥50% PSA decrease. Meta-analysis of the HRs of OS according to any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

CONCLUSIONS

PRLT results in higher proportion of patients responding to therapy based on ≥50% PSA decline compared to controls. Any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

ADVANCES IN KNOWLEDGE

This is the first meta-analysis to aggregate the recent randomized controlled trials of PRLT which shows CRPC patients had a higher response to therapy after PRLT compared to controls.

Dosimetry in Lu-177-PSMA-617 prostate-specific membrane antigen targeted radioligand therapy: a systematic review

BACKGROUND

177Lu-prostate-specific membrane antigen (PSMA) gained popularity as a choice of agent in the treatment of patients with advanced prostate cancer or metastatic castration-resistant stage of prostate carcinoma (mCRPC) diseases. However, this treatment may cause fatal effects, probably due to unintended irradiation of normal organs. We performed an extensive systematic review to assess the organs at risk and the absorbed dose received by tumor lesions in 177Lu-PSMA therapy.

DESIGN

In this review, published peer-reviewed articles that cover clinical dosimetry in patients following peptide radionuclide ligand therapy using 177Lu-PSMA have been included. Two senior researchers independently checked the articles for inclusion. A systematic search in the database was made using PubMed, Publons and DOAJ. All selected articles were categorized into three groups: (1) clinical studies with the technical description of dosimetry in 177Lu-PSMA therapy (2) organ dosimetry in 177Lu-PSMA therapy or (3) tumor dosimetry in 177Lu-PSMA therapy.

RESULT

In total, 182 citations were identified on PSMA therapy and 17 original articles on 177Lu-PSMA dosimetry were recognized as eligible for review. The median absorbed dose per unit of administered activity for kidneys, salivary, liver, spleen, lacrimal and bone marrow was 0.55, 0.81, 0.1, 0.1, 2.26 and 0.03 Gy/GBq, respectively. The median absorbed dose per unit of activity for tumor lesions was found in a range of 2.71-10.94 Gy/GBq.

CONCLUSION

177Lu-PSMA systemic radiation therapy (SRT) is a well-tolerated and reliable treatment option against the management of the mCRPC stage of prostate carcinoma. Lacrimal glands and salivary glands are the major critical organs in 177Lu-PSMA SRT. Besides, tumors receive 3-6 times higher absorbed doses compared to organs at risk.

Hematotoxicity and Nephrotoxicity in Prostate Cancer Patients Undergoing Radioligand Therapy with [177Lu]Lu-PSMA I&T

Simple Summary

Radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-directed agents has shown remarkable results in patients with advanced prostate cancer. Our objective was to provide data on the side effect profile of PSMA-directed RLT using the therapeutic radiotracer [¹⁷⁷Lu]Lu-PSMA I&T. We evaluated patients with castration-resistant metastatic prostate cancer treated with at least three cycles of [¹⁷⁷Lu]Lu-PSMA I&T. A substantial fraction of the patients already had impaired renal function and/or reduced white blood cell counts at baseline, but the degree of nephrotoxicity or hematotoxicity under RLT was low. No severe toxicities occurred under RLT.

Abstract

(1) Background: Prostate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) has shown remarkable results in patients with advanced prostate cancer. We aimed to evaluate the toxicity profile of the PSMA ligand [¹⁷⁷Lu]Lu-PSMA I&T. (2) Methods: 49 patients with metastatic, castration-resistant prostate cancer treated with at least three cycles of [¹⁷⁷Lu]Lu-PSMA I&T were evaluated. Prior to and after RLT, we compared leukocytes, hemoglobin, platelet counts, and renal functional parameters (creatinine, eGFR, n = 49; [^99mTc]-MAG3-derived tubular extraction rate (TER), n = 42). Adverse events were classified according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0 and KDIGO Society. To identify predictive factors, we used Spearman’s rank correlation coefficient. (3) Results: A substantial fraction of the patients already showed impaired renal function and reduced leukocyte counts at baseline. Under RLT, 11/49 (22%) patients presented with nephrotoxicity CTCAE I or II according to creatinine, but 33/49 (67%) according to eGFR. Only 5/42 (13%) showed reduced TER, defined as <70% of the age-adjusted mean normal values. Of all renal functional parameters, absolute changes of only 2% were recorded. CTCAE-based re-categorization was infrequent, with creatinine worsening from I to II in 2/49 (4.1%; GFR, 1/49 (2%)). Similar results were recorded for KDIGO (G2 to G3a, 1/49 (2%); G3a to G3b, 2/49 (4.1%)). After three cycles, follow-up eGFR correlated negatively with age (r = −0.40, p = 0.005) and the eGFR change with Gleason score (r = −0.35, p < 0.05) at baseline. Leukocytopenia CTCAE II occurred only in 1/49 (2%) (CTCAE I, 20/49 (41%)) and CTCAE I thrombocytopenia in 7/49 (14%), with an absolute decrease of 15.2% and 16.6% for leukocyte and platelet counts. Anemia CTCAE II occurred in 10/49 (20%) (CTCAE I, 36/49 (73%)) with a decrease in hemoglobin of 4.7%. (4) Conclusions: After PSMA-targeted therapy using [¹⁷⁷Lu]Lu-PSMA I&T, no severe (CTCAE III/IV) toxicities occurred, thereby demonstrating that serious adverse renal or hematological events are unlikely to be a frequent phenomenon with this agent.

Radiation Dosimetry in 177Lu-PSMA-617 Therapy

Radionuclide therapy using the small molecule PSMA bound to the beta-emitting radionuclide, Lutetium-177 (¹⁷⁷Lu-PSMA) has demonstrated efficacy and survival benefit castrate resistant metastatic disease and represents a novel new line of therapy. Whilst dosimetry was critical for early development, it was not incorporated into either the TheraP or VISION randomized studies, highlighting the difficulty of adopting dosimetry in routine clinical practice. Accumulated clinical experience has also shown that the common (and generally low grade) toxicities such as nausea, xerostomia, and cytopenias are not readily predicted on the basis of dosimetry estimates. The majority of dosimetry and clinical literature deals with the radiopharmaceutical ¹⁷⁷Lu-PSMA-617 which displays relatively consistent patterns of retention among normal tissues and high specificity for metastatic prostate cancer phenotypes. Population dosimetry incorporating estimates to the kidneys, salivary glands, and bone marrow have been widely reported the typical range of doses is becoming well established. There is growing interest on tumor dosimetry in ¹⁷⁷Lu-PSMA-617 therapy as an overall modest side-effect profile from primary organ retention has been observed. A focus away from normal organ dosimetry to whole body tumor dosimetry may enable early prediction of treatment failure. Given the safety of ¹⁷⁷Lu-PSMA there is also potential to escalate administered radioactivity to further improve outcomes. Importantly, the variability of uptake between individuals, both to tumor and normal organs, has also been highlighted which provides some rationale for the utility of personalized radiation analysis to optimize treatment based on potential toxicity thresholds or tumor control. Methods to perform dosimetry using serial post treatment imaging may incorporate planar, 3D SPECT, or hybrid datasets. Reliable measurements may be obtained through either method, however, continued developments in computational analysis are better suited to fully 3D imaging; particularly in conjunction with volumetric CT to assist with alignment and contouring. Dose analysis over sequential treatment cycles is vital to understand the radiobiology of these treatments which is unique compared to external beam therapy due to dose rate, fractionation scheme, and potential for intratumoral nonuniformity.

Renal and Salivary Gland Functions after Three Cycles of PSMA-617 Therapy Every Four Weeks in Patients with Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

[¹⁷⁷Lu]Lu-PSMA-617 radioligand therapy (PSMA-RLT) could affect kidney and salivary gland functions in metastatic castration-resistant prostate cancer (mCRPC) patients.

METHODS

We retrospectively analyzed clinical, renal, and salivary scintigraphy data and salivary [⁶⁸Ga]Ga-PSMA-11 ligand PET scan measures such as metabolic volume and SUVmax values of 27 mCRPC men (mean age 71 ± 7 years) before and 4 weeks after receiving three cycles of PSMA-RLT every 4 weeks. Twenty-two patients additionally obtained renal and salivary scintigraphy prior to each cycle. A one-way ANOVA, post-hoc Scheffé test and Cochran's Q test were applied to assess organ toxicity.

RESULTS

In total, 54 PSMA PET scans, 98 kidney, and 98 salivary scintigraphy results were evaluated. There were no significant differences for the ejection fraction, peak time, and residual activity after 5 min for both parotid and submandibular glands prior to each cycle and 4 weeks after the last cycle. Similarly, no significant differences in serum creatinine and renal scintigraphy parameters were observed prior to each cycle and 4 weeks after the last treatment. Despite there being no changes in the metabolic volume of both submandibular glands, SUVmax values dropped significantly (p < 0.05).

CONCLUSION

Results evidenced no alterations in renal function and only minimal impairment of salivary function of mCRPC patients who acquired an intense PSMA-RLT regimen every 4 weeks.

Outcome of 177Lu-PSMA-617 Radioligand Therapy in Chemo-Refractory Patients with Metastatic Castration-Resistant Early-Onset Prostate Cancer

Simple Summary

The risk of prostate cancer development, the second most commonly occurring cancer in men overall, increases strongly with age. About 10% of patients, however, are diagnosed with early-onset prostate cancer (age at diagnosis: ≤55 years). This is considered to be a distinct clinical and pathological phenotype with a poor prognosis. Generally, prostate cancer cells express high quantities of prostate-specific membrane antigen (PSMA) on their surface. Radioligand therapy is a type of treatment, which, among other available agents, uses the beta-emitting radionuclide ¹⁷⁷Lutetium (¹⁷⁷Lu) and a PSMA-targeting ligand termed PSMA-617 for internal irradiation of metastatic prostate cancer cells. The aim of our retrospective study was to assess the efficacy and safety of radioligand therapy with ¹⁷⁷Lu-PSMA-617 in early-onset metastasized castration-resistant prostate cancer patients refractory to chemotherapy. Special emphasis was placed on the patients’ response to the treatment and survival. The study provides support for the expected shorter survival compared to heterogenous patient groups.

Abstract

The aim of this retrospective study was to assess the outcome of patients with metastasized castration-resistant early-onset prostate cancer refractory to chemotherapy receiving radioligand therapy with ¹⁷⁷Lutetium-PSMA-617 (LuPSMA-RLT). Twenty-five patients of ≤55 years of age at prostate cancer diagnosis, treated with a median of four (IQR 2–6) cycles (mean of 7.7 ± 1.4 GBq per cycle) every 6–8 weeks, were analyzed. Survival outcome was calculated based on the Kaplan–Meier method. The median progression-free survival (PFS) was 3.8 months (95% CI 2.3–5.3), and overall survival (OS) was 8.5 months (95% CI 6.2–10.8). An initial PSA reduction (≥ 50%) was observed in 9/25 (36%) of patients without being significantly associated with OS (p = 0.601). PSA response (PSA decline ≥50% at 12 weeks) was observed in 12/25 (48%) of patients and significantly associated with longer OS (16.0 months, 95% CI 7.4–24.6 vs. 4.0 months, 95% CI 1.1–6.9, p = 0.002). Imaging-based response using ⁶⁸Ga-PSMA-11-PET/CT after two to three cycles was seen in 11/25 (44%). Additionally, responders had a significantly longer median PFS (8.7 months, 95% CI 1.3–16.1 vs. 1.9 months, 95% CI 1.7–2.2, p < 0.001) and OS (16.0 months, 95% CI 7.6–24.4 vs. 4.0 months, 95% CI 0.9–7.1; p = 0.002). Intra- or post-therapeutic toxicity was graded according to the CTCAE v5.0 criteria. Newly developing grade ≥ 3 anemia, leukopenia, and thrombocytopenia occurred in three (12%), one (4%), and three (12%) patients, respectively. One patient showed renal toxicity (grade ≥ 3) during follow-up. Pain palliation (>2 level VAS decline) was achieved in 9/14 (64%) and performance status improvement (ECOG level decline ≥ 1) in 8/17 (47%) of patients. Compared to previous reports, radioligand therapy with ¹⁷⁷Lu-PSMA-617 in metastasized castration-resistant early-onset prostate cancer patients refractory to chemotherapy yields similar response rates with a comparable safety profile, but is associated with shorter survival.